This article proposes a split-phase flipping-capacitor rectifier (SPFCR) to resolve the hard tradeoff between the number of capacitors and the energy-extraction efficiency for capacitive piezoelectric energy-harvesting (PEH) interfaces. By splitting the capacitor usage into multiple phases, this article can achieve the most number of flipping phases using the same number of capacitors when compared with the state of the art. We also relaxed the implementation complexity by removing insignificant SFPCR flipping phases without sacrificing the energy-harvesting efficiency. To improve further the input power adaptation, the flipping capacitors are reconfigured as a multiple-voltage-conversion-ratio (MVCR) switched-capacitor dc–dc converter during the non-flipping period without using extra passives. Maximum-power-point tracking (MPPT) is also accomplished using the full-bridge rectifier (FBR) fractional open-circuit voltage ( VOC,FBR ) to relax the voltage-tolerance requirements. Fabricated in 0.18- μm CMOS, the proposed 21-phase SPFCR PEH interface demonstrates a measured maximum output power improving rate (MOPIR) of up to 9.3 × with VD=0.12 V (6.5 × with VD=0 V) when compared with the conventional FBR interface over an equivalent FBR input power range ( Pin, FBR ) from 0.15 to 5.57 μW .